amaps

mem/page.c

@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: ISC
+
+#include <zinnia/alloc.h>
+#include <zinnia/atomic.h>
+#include <zinnia/park.h>
+#include <zinnia/virt.h>
+
+struct page* vm_page_from_addr(phys_t addr) {
+    return &vm_pfndb[addr / arch_mem_page_size()];
+}
+
+errno_t page_alloc(enum alloc_flags flags, struct page** out) {
+    phys_t addr;
+    errno_t status = mem_phys_alloc(1, flags, &addr);
+    if (status)
+        return status;
+
+    struct page* page = vm_page_from_addr(addr);
+    page->type = PAGE_PHYS;
+    page->obj.owner = nullptr;
+    page->obj.index = 0;
+    atomic_store(&page->flags, 0, ATOMIC_RELAXED);
+    atomic_store(&page->holds, 1, ATOMIC_RELEASE);
+    *out = page;
+    return 0;
+}
+
+void page_hold(struct page* page) {
+    atomic_fetch_add(&page->holds, 1, ATOMIC_RELAXED);
+}
+
+void page_unhold(struct page* page) {
+    if (atomic_fetch_sub(&page->holds, 1, ATOMIC_RELEASE) != 1)
+        return;
+    atomic_fence(ATOMIC_ACQUIRE);
+    atomic_store(&page->flags, 0, ATOMIC_RELAXED);
+    page->obj.owner = nullptr;
+    mem_phys_free(vm_page_addr(page), 1);
+}
+
+bool page_try_busy(struct page* page) {
+    return !(atomic_fetch_or(&page->flags, PAGE_BUSY, ATOMIC_ACQUIRE) & PAGE_BUSY);
+}
+
+void page_unbusy(struct page* page) {
+    const uint32_t old = atomic_fetch_and(&page->flags, ~(PAGE_BUSY | PAGE_WANTED), ATOMIC_RELEASE);
+    if (old & PAGE_WANTED)
+        unpark_all(&page->flags, 0);
+}
+
+static bool still_busy(void* ctx) {
+    struct page* page = ctx;
+    uint32_t flags = atomic_load(&page->flags, ATOMIC_RELAXED);
+    while (flags & PAGE_BUSY) {
+        if (atomic_compare_exchange_weak(&page->flags, &flags, flags | PAGE_WANTED, ATOMIC_RELAXED, ATOMIC_RELAXED))
+            return true;
+    }
+    return false;
+}
+
+void page_wait(struct page* page) {
+    park(&page->flags, still_busy, page, 0);
+}